This application claims the priority of Japanese Patent Application No. 2000-093068 filed on Mar. 30, 2000, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an unsophisticated data-imprinting optical system which can be applied to a camera capable of optically imprinting photographing data, such as a date, onto a film negative.
2. Description of the Prior Art
A system for a camera which enables imprinting of photographing data, such as a date, onto a film negative has hitherto been known, and imprinting of photographing data is one of the important functions of the camera.
Since long ago, such a system has been constructed such that a numerical string of a manually-set date is optically imprinted onto a film negative by means of a simple shutter which controls a projection lens and an exposure time. This system suffers a problem of a battery cell being depleted by an illumination lamp. Recent proliferation of a light source system which operates at an extremely-feeble electric current, such as an LED or liquid crystal, obviates the problem. Hence, the majority of cameras are equipped with this system. However, the system recently encounters a new problem, and another system capable of solving the new problem has recently been adopted.
In association with recent, rapid miniaturization of a camera, a limit is imposed on a space for positioning a data-imprinting optical system, and there arises a necessity for directly illuminating a numerical string or a string of characters by means of an LED or liquid crystal. The limit and the necessity account for the new problem. If a string of characters to be displayed is long, upsizing of a display element, such as an LED or liquid crystal, arises in addition to a problem of space. Accordingly, there arises a problem of inevitable use of a battery cell of large capacity, in addition to a cost problem. To solve the problems, there is employed a system which imprints data on a film negative, by means of illuminating a string of LEDs in a time sequence in the manner of a light sign board, and successively exposing the film in a time sequence through utilization of an automatic film take-up operation of the camera. This system involves use of only a single string of light sources. Traveling speed of a film negative rather than a shutter determines an exposure time, thereby imprinting data very efficiently. This is described in, for example, Japanese Unexamined Patent Publication No. 9(1997)-304823.
Such a data-imprinting optical system requires only an object size corresponding to the size of a single line of LEDs. The optical system has a narrow angle of view, and the only requirement is that image quality in the vicinity of center of the angle of view be compensated. Accordingly, sufficient performance of the optical system can be achieved by use of a single biconvex lens.
The foregoing system is predicated on an automatic film advancing operation of a camera. For this reason, the system cannot be applied to a low-cost, unsophisticated camera of manual-advance type which has recently become pervasive. The manual-advance camera involves indefinite film advance, which is very likely to result in unevenness in exposure of a character string.
An unsophisticated camera of manual advance type which has recently become pervasive requires a necessity of exposing data to be imprinted in the form of a regular character string by a single exposing operation. As a matter of course, strong demand has existed for miniaturizing such an unsophisticated camera. In contrast with the data-imprinting camera described previously, the unsophisticated camera encounters difficulties in reducing an imaging factor and the angle of view of a character string and constructing a projection lens from a single biconvex lens, which would otherwise increase an optical path length and hinder miniaturization of a camera.
Difficulties are encountered in direct application of the related-art technique to a data-imprinting optical system of an unsophisticated camera of manual advance type which has currently become pervasive. Therefore, development of a new data-imprinting optical system has been desired.
In connection with such a desire, there has been known a technique for exposing all display data within a single period of exposure time by a single operation, as described below.
Several methods for introducing extraneous light into the data-imprinting optical system are described in Japanese Unexamined Patent Publication No. 10(1998)-073878. Particularly, the publication includes a description about a lens-equipped camera of film type having a liquid-crystal display imprinting function. Back light is usually used for liquid crystal display. However, a camera is made inexpensive by use of the intensive extraneous light collected by a condenser lens. The technique has great value as a light-source system of a data impinging optical system. However, no contrivance has been made on the technique for realizing miniaturization of and space-saving in the camera.
Japanese Unexamined Patent Publication No. 10(1998)-254099 also describes a lens-equipped camera of film type having a liquid-crystal display imprinting function. More specifically, the publication describes a technique for collecting extraneous light on a liquid-crystal display surface more efficiently. However, this publication also fails to describe a contrivance to enable miniaturization of and space-saving in the camera.
The present invention has been conceived against the foregoing backdrop and is aimed at providing a data-imprinting optical system which can be applied to a low-cost, unsophisticated camera of manual film advance type and enables miniaturization of and space-saving in the camera.
Accordingly, the present invention provides a data-imprinting optical system which imprints, onto a film surface, data appearing on a photographing information/data display member located on the part of an object relative to the film surface and which is separate from a photographing lens, wherein
the optical system comprises one meniscus lens having a positive refractive power and a brightness aperture and satisfies conditional expressions (1) through (3) provided below:
3.9xe2x89xa6L/F less than 5.0xe2x80x83xe2x80x83(1)
0.02 less than D1/F less than 0.10xe2x80x83xe2x80x83(2)
xe2x88x920.5 less than R3/F less than xe2x88x920.2xe2x80x83xe2x80x83(3)
where,
L: distance from the photographing data display member to the film surface along the optical axis of a photographing lens,
F: focal length of the meniscus lens,
D1: distance from the aperture to the surface of the meniscus lens facing the aperture along the optical axis of the data-imprinting optical system, and
R3: the radius of curvature of the surface of the meniscus lens opposite that facing the aperture (a paraxial radius of curvature in a case where the surface is an aspherical surface).
Preferably, the meniscus lens is formed from an organic material, and the surface of the meniscus lens opposing the photographing information/data display member is aspherically concave. Further, the aperture is preferably located on the part of the meniscus lens opposing the photographing information/data display member.
Preferably, a conditional equation (4) provided below is satisfied when the angle of inclination assumes a positive value in a case where an optical axis of a photographing optical system moves away from an optical axis of the data-imprinting optical system as the data-imprinting optical system approaches the film surface:
0.0xc2x0xe2x89xa6xcex8 less than 10.0xc2x0xe2x80x83xe2x80x83(4)
Preferably, the data display member is disposed opposite the optical axis of the photographing optical system with reference to the optical axis of the data-imprinting optical system, and a conditional equation (5) provided below is satisfied, given that the minimum distance between the optical axis of the data-imprinting optical system and the data display member within a plane perpendicular to the optical axis of the data-imprinting optical system is taken as H:
0.0 less than H/F less than 0.5xe2x80x83xe2x80x83(5)
Preferably, the data display member is included, and a conditional equation (6) provided below is satisfied, given that, when the surface of the data display member is inclined so as to approach the film surface as the data display member moves away from the optical axis of the photographing optical system within the plane perpendicular to the optical axis of the photographing optical system, the angle of inclination is taken as xcex8d and the direction in which the inclination becomes greater is taken as positive:
0.0xc2x0xe2x89xa6xcex8d less than 10.0xc2x0xe2x80x83xe2x80x83(6)
Preferably, the center of the aperture is made closer to the optical axis of the photographing lens within a plane perpendicular to the optical axis of the data-imprinting optical system, and the geometry of the brightness aperture is defined such that an area equivalent to that of an aperture capable of satisfying desired brightness can be ensured and such that the aperture is made longer in one direction than in another direction.
The data-impinging optical system according to the present invention imprints display data on a film negative from the direction of an object for the following reasons. For example, if a character string for the display data corresponds to a date, at least seven characters are required; i.e., two numerals for a year, at least one for a month, two numerals for a date, and spaces between the three fields. If the character string is displayed through use of a light-source system, a considerable space is required. Further, a substrate suitable for use in displaying data, such as a circuit, also becomes bulky, which in turn requires a larger space. A room for such a space is not available on a back cover of a camera opposing a reverse side of a film negative. For this reason, there is no alternative but to imprint data on a film surface by way of a photographing lens through exposure. In fact, a date-imprinting optical system of early type doubles as a display to be indicated in a viewfinder. A character string equipped with an illumination light source is disposed at an upper part of the viewfinder. The character string is imprinted on the front surface of a film negative by way of the inside of the viewfinder, a film box, and a mirror through exposure. To this end, a large number of optical components are required, which poses a problem of cost or alignment of an optical axis. The data-imprinting optical system according to the present invention must be constructed so that it can be applied to a low-cost unsophisticated camera. Hence, such a layout of the optical system is not allowed. Therefore, projection of a character string directly on the front surface of the film negative from the front side of the camera is indispensable.
In the case of a recent camera, particularly a compact camera, a main camera unit is made thin, and direct imprinting of data onto a film negative requires a considerably short conjugate distance. At this time, a character string for data cannot be made smaller than a certain size, for reasons of brightness. Hence, a relatively wide view angle is required. Moreover, a character string serving as display data must be projected on a specific location on a film surface. Hence, a desirable location is a lower corner on a film negative at which the character string will not hinder exposure of an object image. For this reason, the data-imprinting optical system must be provided so as to avoid a luminous flux of the photographing lens.
The operation of the present invention will be described by reference to claims.
Claim 1 provides basic requirements for embodying a data-imprinting optical system according to the present invention. More specifically, the optical system is independent of a photographing lens. The optical system comprises a photographing information/data display member located on the part of a film surface opposing an object, and a single positive meniscus lens. The optical system imprints display data onto a film. So long as the following three conditional equations are satisfied, the optical system enables projection of data onto a film negative inexpensively and with high performance.
Conditional equation (1) enables layout of the data-imprinting optical system on the front side of the camera. More specifically, the equation defines the relationship between the focal length F of a meniscus lens and a distance L between the photographing information/data display member and the film surface with reference to the optical axis of the photographing lens. Here, the focal length F substantially corresponds to the conjugate length of the data-imprinting optical system. Provided that the distance between the principal points of a lens is disregarded and that an imaging factor is equi-magnification, the shortest conjugate length of a lens having the focal length F is 4F. The lower limiting value of the equation is defined in consideration of inclination of the data-imprinting optical system relative to the optical axis of the photographing lens. The lower limiting value is substantially equi-magnification. In contrast, the upper limit value of the equation corresponds to an imaging factor of about xc3x972.6 or xc3x970.4. If the upper limiting value is exceeded, the data-imprinting optical system moves away from the film surface, which is preferable in terms of lens layout. Concurrently, required positional accuracy of a lens (when the imaging factor is xc3x972.6 magnification or greater) becomes excessively stringent, or the lens approaches too closely to the film surface, thereby rendering layout of the lens excessively difficult (when the imaging factor is xc3x970.4 magnification or less).
Conditional equations (2) and (3) are for realizing an optical system having a wide view angle in the vicinity of equi-magnification and making appropriate the geometry of the data-imprinting optical system which establishes an anastigmatic relationship between an abaxial luminous flux and the aperture, as well as making appropriate the positional relationship between the aperture and the lens. If Equation (2) assumes a value which is lower than the lower limiting value thereof, a distance D1 between the aperture and the lens becomes too small, thereby resulting in an excessively large astigmatism. As a result, the anastigmatic relationship is lost, with the result that uniform imaging performance is not achieved. If Equation (2) assumes a value greater than the upper limiting value thereof, the aperture becomes excessively distant from the lens, thereby rendering the data-imprinting optical system bulky and hindering space saving. If Equation (3) assumes a value lower than the lower limiting value thereof, the surface of the meniscus lens distant from the aperture assumes an excessively-large negative radius of curvature R3 (or a paraxial radius of curvature if the surface is aspheric), and field tilt arises, thereby losing the anastigmatic relationship. As a result, uniform imaging performance is not achieved. In contrast, if Equation (3) assumes a value higher than the upper limiting value thereof, a field curvature is excessively corrected, thereby deteriorating an imaging characteristic of the optical system.
Consequently, the principal object of the present invention; that is, a data-imprinting optical system having a short conjugate length, a wide view angle, and a uniform imaging characteristic, can be achieved, so long as the foregoing three conditional equations (1) through (3) are satisfied.
Claim 2 defines the configuration of a data-imprinting optical system for reducing costs and improving the performance of the optical system to a much greater extent. The aperture is disposed on a part of the photographing information/data display member, and hence the surface of the meniscus lens opposing the meniscus lens is concave. The principal point of the lens is moved to a point on the part of an image surface. Hence, even at the time of equi-magnification, the lens is located offset toward the display member, thereby yielding an advantage in terms of layout of a lens. As a result of the surface of the meniscus lens opposing the aperture (i.e., the surface of the meniscus lens remaining in contact with the aperture) being formed into an aspherical lens, spherical aberration and coma aberration are corrected. Further, so long as the meniscus lens is formed from an organic material, lens cost can be diminished. Consequently, a reduction in cost and improvement in performance of the data-imprinting optical system can be achieved by means of satisfying the requirements described in claim 2.
Claims 3 through 6 define requirements for arranging the data-imprinting optical system such that no interference arises between a luminous flux of the data-imprinting optical system and a luminous flux of the photographing optical system.
If conditional equation (4) defined in claims 3 and 4 assumes a value lower than the lower limiting value thereof, the advantage concerning the lens layout cannot be yielded. In contrast, if conditional equation (4) assumes a value greater than the upper limiting value thereof, there is yielded an advantage in terms of layout of a lens. However, the view angle of the photographing information/data display member becomes excessively larger than that of the data-imprinting optical system. According to a rule of the fourth power of the cosine, an imbalance arises in the amount of ambient light, and an unbalanced drop in the amount of light undesirably arises. The tilt of an imprinted image is made greater by perspective, thereby deteriorating the performance of forming an image on a film surface.
Claims 5 and 6 define requirements for arranging the photographing information/data display member at a point on the optical axis of the photographing lens away from the optical axis of the data-imprinting optical system. For the same reasons described in connection with claims 3 and 4, there can be yielded an advantage in terms of layout of a lens. If conditional equation (5) assumes a value lower than the lower limiting value thereof, difficulty is encountered in yielding the advantage. In contrast, if conditional equation (5) assumes a value higher than the upper limiting value thereof, the view angle becomes excessively large, with the result that a drop in the amount of ambient light arises and field tilt arises. Consequently, the imaging performance of the optical system is deteriorated.
Claim 7 yields a working-effect and an advantage; that is, ability to correct field tilt by utilization of perspective and an improvement in performance, by means of inclining the photographing information/data display member relative to the optical axis of the data-imprinting optical system, and, by extension, to the optical axis of the photographing lens. If conditional equation (6) assumes a value lower than the lower limiting value thereof, no advantage is yielded or a reverse effect will arise. In contrast, if conditional equation (6) assumes a value greater than an upper limiting value, the view angle becomes excessively large, and a drop in the amount of ambient light arises or excessive field tilt arises, thereby deteriorating the imaging performance of the optical system. In a camera, such as a lens-equipped film, which has a film surface curved in a longitudinal direction, the corner of the film surface at which data are to be imprinted is tilted, thus enabling correction of field tilt.
Claim 8 defines deviation of the center of the aperture or change in the size of the aperture depending on a direction. As a result, the imaging performance of the optical system is improved, thereby increasing the focal depth. For instance, the focal depth is small in the sagittal direction, the length of an opening of the aperture is increased in the tangential direction, and the length of the opening of the aperture is shortened in the sagittal direction. Consequently, the focal depth in the tangential direction is made slightly shallow. However, the focal depth of the overall optical system in the sagittal direction can be increased.